1. Field of the Invention
The invention relates to a method for adjusting focal point's positions of an intraocular implant and a device for the method, and more particularly to a method for adjusting focal point's positions of an intraocular implant, which is an artificial lens to be inserted in a human eyeball in place of crystalline lens extracted therefrom, and a device for use in the adjusting method.
2. Description of the Related Art
Human eyes essentially include eyeballs and optic nerve. These and appendages of eyeballs, i.e., eyelids, supercilium, conjunctiva, lacrimal apparatus and muscles of the eyeballs constitute the organ of vision. The outer wall of eyeballs comprises three layers of outer, middle and inner membranes, the outer membrane having cornea and sclera, the middle membrane having iris, ciliary body and choroid, and the inner membrane having retina. The eyeballs are filled substantially with a vitreous body and have crystalline lens before the vitreous body. A space between the crystalline lens and cornea is filled with aqueous humor.
The crystalline lens is an organ in the shape of biconvex lens and positioned centrally of the front half of the eyeball. Any objects placed near or far from human-eyes are focused into an image on the retina by the crystalline lens. For adjusting the crystalline lens to the objects near the eyes, ciliary muscle contracts to relax Zinn's zonule, which is in the shape of a flowery crown to sorround the crystalline lens, so that the crystalline lens becomes free of pulling by Zinn's zonule and increases in thickness due to elasticity of the crystalline lens itself. Thus, the adjusted crystalline lens can have the same function as of an optical lens of a short focal length. When the crystalline lens is adjusted to objects placed far from human eyes, ciliary muscle relaxes to tense Zinn's zonule, so that the crystalline lens is applied with a pulling force to be made thin and flat, thereby having the same function as an optical lens of a long focal length.
As above, the human eyes are exquisite, and the crystalline lens can be adjusted to the short or long range of scope by contracting or relaxing ciliary muscle to have separate focal point's positions and also to be increased or decreased in refraction factor as known.
Patients with cataracts suffer from troubles in eyesight by opacity of crystalline lens which has the above important function. Surgically extracting the opaque crystalline lens placed centrally of the front half of eyeballs is the only effective means for recovering the patients' eyesight at the present time. The eyes from which the crystalline lens is extracted and removed are the so-called "artificial aphakia" and cannot focus outside objects into images on retina at far distances (highly insufficient in refraction factor). Hence, merely extracting the opaque crystalline lens does, generally, not lead to recovery of good eyesight, and any lens means, such as spectacles or contact lens hitherto used, for supplementing the insufficient refraction factor is required to be applied. And now most widely made use of and popular is the method inserting an artificial lens into the eyes in place of crystalline lens extracted therefrom, i.e., use of the "intraocular implant" which enables recovery of eyesight to the extent nearest the inherent visual capacity.
Next, explanation will be given in more details with referring to FIGS. 17 to 21.
FIG. 17 is a cross-sectional view of a human eyeball, FIG. 18 a cross-sectional view of the same in normal vision, FIG. 19 a cross-sectional view of the same in near sightedness, FIG. 20 a cross-sectional view of the same in far sightedness, and FIG. 21 a cross-sectional view of the same wherein an intraocular implant is inserted.
In FIG. 17, 51 is cornea, a transparent membrane extending at the front of eyeballs and shaping a part of spheroid with radius of crook of about 8 mm. 52 is aqueous humor filled in the space between cornea 51 and crystalline lens 54. 53 is iris, a disc-like membrane equivalent to the diaphragm of cameras and having almost centrally a round hole (pupil) which is made smaller or larger corresponding to the amount of lights passing therethrough or by any other causes.
54 is a lens, having the most important function in the eyeball, and 55 is a ciliary body which causes the ciliary muscle to function for adjusting the crystalline lens 54 to focus at short and long ranges. It is known that the crystalline lens 54 in this instance does change curvature mainly on the front surface (at the side of cornea) but not on both surfaces, i.e., the front surface and the rear surface (at the side of retina).
57 is vitreous body made of a transparent sol substance filled, almost wholly in the eyeball, and refraction factor is 1.334. 58 is retina and 59 is optic nerve which transmits to cerebrum any signals of images focused on the retina 58.
FIG. 18 shows the focusing on retina in normal vision wherein any object placed far from the eye is focused into an image on retina. FIG. 19 shows the focusing in vitreous body before retina, i.e., the state of near sightedhess wherein any two objective points spaced from each other at a very small distance cannot be sensed, just as two points, on the retina. In addition, FIG. 20 shows the focusing behind retina, the opposite of FIG. 19, i.e, the state of far sightedhess wherein distinct vision is not obtainable as in near sightedness shown in FIG. 19.
FIG. 21 is a cross-sectional view of an eyeball wherein opaque crystalline lens 54 causing visual disturbance is extracted and an intraocular implant is inserted. 60 is the in intraocular implant made of a polymeric material, and 61 is a loop for fixing the intraocular implant in position in the eyeball.
In the meantime, the aging society has increased the number of patients with cataracts, and of operations for extraction of the opaque crystalline lens and insertion of an artificial lens (intraocular implant) for recovery of eyesight.
The intraocular implant is made of a polymeric material, for example, polymethyl methacrylate A (PMMA) and has a fixed focus, so that the lens cannot freely focus at any positions on retina, as the crystalline lens of human eyes does from the so-called distance of distinct vision (scope in short range) to infinite vision (scope in long range). It is naturally possible in use of the intraocular implant for the subject to make his eyes half-shut or make pupil smaller so as to have higher focal depth, thereby improving his vision to a certain extent. But, this is limited due to the fixed focus of the intraocular implant. Furthermore, there has been such problem that the conventional intraocular implant can "supplement insufficient refraction factor" but not "adaptation capacity", the separate important function of crystalline lens, due to functional insufficiency of the intraocular lens in comparison with crystalline lens.